Assembly including carrier for devices

ABSTRACT

U.S. Pat. No. 3,533,155, whereof this is a division, concerns a method of bonding which employs a compliant or deformable medium to hold workpiece devices during bonding, the medium transmitting bonding energy to the workpieces and deforming about the workpieces. The invention of this division relates to the compliant medium and to an assembly, useful in compliant bonding of the type described in U.S. Pat. No. 3,533,155. The assembly is provided by the compliant medium plus the devices for which the medium acts as a temporary retainer or carrier. The compliant medium takes the form of a flat sheet of a readily deformable material, such as an elongated tape or ribbon of a metal or an alloy with an oxide surface film. The medium has a thickness substantially greater than workpieces to be bonded. Upper surfaces of the workpieces are secured to the under surface of the medium, for example, by an adhesive. The workpieces are positioned in fixed relationship to one another, preferably in spaced apertures in the medium. Indexing means may also be present in the tape or ribbon of the compliant medium.

States atent Coucoulas [1 1 3,655,177 [4 1 Apr.11,1972

[72] Inventor: Alexander Coucoulas, Bridgewater Township, Somerset County, NJ.

[73] Assignee:

New York, NY.

[22] Filed: Oct. 20, 1969 [21] Appl. No.: 870,754

Related U.S. Application Data [62] Division of Ser. No. 651,411, July 6, 1967, Pat. No.

[52] U.S. Cl ..269/1, 156/540, 228/4 [51] Int. Cl ..B25b 11/00 [58] Field of Search "269/37, 45, 206, 274, 286,

Western Electric Company Incorporated,

FOREIGN PATENTS OR APPLICATIONS 213,145 3/1924 Great Britain Primary Examiner-Frank T. Yost Attorney-H. J. Winegar, R. P. Miller and W. M. Kain [5 7] ABSTRACT U.S. Pat. No. 3,533,155, whereof this is a division, concerns a method of bonding which employs a compliant or deformable medium to hold workpiece devices during bonding, the medium transmitting bonding energy to the workpieces and deforming about the workpieces. The invention of this division relates to the compliant medium and to an assembly, useful in compliant bonding of the type described in U.S. Pat. No. 3,533,155. The assembly is provided by the compliant medium plus the devices for which the medium acts as a temporary retainer or carrier. The compliant medium takes the form of a flat sheet of a readily deformable material, such as an elongated tape or ribbon of a metal or an alloy with an oxide surface film. The medium has a thickness substantially greater than workpieces to be bonded. Upper surfaces of the work pieces are secured to the under surface of the medium, for example, by an adhesive. The workpieces are positioned in fixed relationship to one another, preferably in spaced apertures in the medium. Indexing means may also be present in the tape or ribbon of the compliant medium.

12 Claims, 13 Drawing Figures nun Patented A ril 11,' 1972 3,655,177

' 2 Sheets-Sheet 1 F/a/A F/6./B

++i+ii\ iiii! INVENTOR A. COUCOUL A8 v MAR/V a JANGARA rH/s ATTORNEYS Patented A ril 11, 1972 3,655,177

2 Sheets-Sheet 2 BACKGROUND OF THE INVENTION This invention relates generally to an assembly and, more particularly, it relates to a carrier and an assembly which may be utilized in the bonding of a first workpiece to one or more second workpieces. The first workpiece may comprise a thin film component or integrated circuit mounted on an insulating substrate, a printed circuit board, or the like. The second workpiece may comprise one or more small wires, the leads from a transistor or integrated circuit device, a small, brittle crystal, or the leads of a beam-lead transistor or integrated circuit device. The assembly of the invention has application to the bonding of workpieces other than the above-described types, but since it is particularly adapted for such workpieces it will be described with reference thereto.

OBJECTS OF THE INVENTION It is a general object of the present invention to provide a new and improved carrier and assembly which may be employed in bonding workpieces.

SUMMARY OF THE INVENTION In essence, the invention of U.S. Pat. No. 3,533,155 is based, at least in part, on the discovery that the use of a compliant or defonnable medium to hold the workpieces has many significant advantages in bonding, and that sufiicient thermal and/or mechanical energy can be transmitted through or absorbed by such a medium to effect a good bond between the workpieces.

A carrier, in the form of a compliant medium, and assembly, which may be utilized in performing the techniques of bonding taught in U.S. Pat. No. 3,533,155, form the subject matter of this invention. The assembly is formed by the combination of a compliant medium and one or more workpiece devices retained or carried by the medium. The compliant medium takes the form of a flat sheet of a readily deformable material. An elongated tape or ribbon of the material, such as a deformable metal or alloy having an adherent oxide film on its surface, may be used as the compliant medium. The medium has a thickness substantially greater than that of workpieces to be bonded. Upper surfaces of the workpieces are preferably secured to the under surface of the medium, for example, by an adhesive. The workpieces may be positioned in fixed relationship to one another, preferably in spaced apertures in the medium. Indexing means may also be present in the tape or ribbon of the compliant medium.

THE DRAWINGS Understanding of the invention will be facilitated by referring to the following detailed description of the several embodiments, in conjunction with the accompanying drawings, wherein:

FIGS. 1A and 1B are side and end elevations, respectively, showing all parts in place for bonding a lead to a substrate by thermocompression bonding in accordance with the invention ofU.S. Pat. No. 3,533,155;

FIGS. 2A and 2B are similar to FIGS. 1A and 1B, showing all parts during thermocompression bonding;

FIGS. 3A and 3B are similar to FIGS. 1 and 2, showing all parts after thermocompression bonding is complete;

FIG. 4 is a side elevation of a beam lead device positioned on a substrate;

FIG. 5 is similar to FIG. 4 and shows the compliant medium in place;

FIG. 6 is a side elevation of the assembly of FIG. 5 during thermocompression bonding in accordance with the invention ofU.S. Pat. No. 3,533,155;

FIG. 7 is a side elevation of the device of FIG. 4 after bonding;

FIG. 8 is a side elevation showing a beam lead device on a substrate ready for ultrasonic bonding in accordance with another embodiment of the invention of U.S. Pat. No. 3,5 33,155

FIG. 9 is a side elevation of the assembly of FIG. 8 during ultrasonic bonding; and

FIG. 10 is a perspective view of a lead frame for a beam lead device or devices for use in thennocompression bonding in accordance with the invention.

DESCRIPTION OF EMBODIMENTS FIGS. 1-3 illustrate bonding of a single lead to a substrate by the first embodiment of the invention of U.S. Pat. No. 3,533,155. An insulating substrate 10 having a metallic land area 12 on the surface thereof is place on a rigid support (not shown). A lead 14 is placed over land area 12 at the desired bonding point. For purposes of illustration, it can be assumed that substrate 10 is a high alumina ceramic,and land area 12 and lead 14 are both gold. The compliant medium is in the form of a wire 16 of a film-forming metal such as aluminum. A heated ram 18 initially clamps the workpieces to the support and, as pressure is applied, wire 16 and lead 14 commence to deform, as shown in FIG. 2. In particular, the line of contact 20 between the two pieces becomes a zone of contact 22, and bulges 24 appear on the unconfined edges of lead 14. At the same time, wire 16 deforms around lead 14. When bonding is complete, as shown in FIG. 3, the initial bulges have been deformed into area 26, and wire 16 has deformed so as to completely cover the entire bond area on both workpieces. The flow of the lead metal in the area 26 against the land metal 12 contributes to the quality of the bond.

When bonding is complete, ram 18 is raised and wire 16 is removed. The existence of the bond can be checked by examination of the impression left in wire 16, which is an exact replica of the bond area. This is of course greatly preferably to the destructive shear-peel test.

The wire 16 will not itself bond to the workpieces because of the tough oxide film on its surface. Since film-forming metals (aluminum, nickel, titanium, tantalum, etc.) always have such oxide films and the thickness thereof can be readily controlled by anodizing, they are preferred as the compliant medium in this embodiment. Other materials can be employed and parting materials used to prevent bonding of the medium to the workpiece, but parting materials will of course be avoided where they might present a contamination problem.

Since gold is a relatively soft metal, compared to aluminum, one might think that the wire 16 would cut right through lead 14 or mash it completely, but this is not the case. Successful bonds of gold leads have even been made using nickel as the compliant medium, which is even harder than aluminum. Of course, when selecting a compliant medium, persons skilled in the art will obviously avoid metals and alloys that would not deform under the bonding conditions.

Bonds produced in the foregoing manner have been determined to be superior to bonds made by conventional ultrasonic and thermocompression techniques. This superiority is both statistical (i.e., the number of good bonds made per thousand) and absolute (i.e., bond strength in a shear-peel test).

FIGS. 4-7 illustrates the bonding of a beam-lead integrated circuit device to a substrate in accordance with the first embodiment of the invention of U.S. Pat. No. 3,533,155. As shown in FIG. 4, the device comprises a silicon chip 28 having gold leads 30 issuing therefrom. It rests on-a substrate 32 having metallic land areas (not shown) under each lead.

As shown in FIG. 5, a hollow perform or lead frame 34 is placed over leads 30 and around device 28. Preform 34 extends substantially above the top of device 28 so that, during bonding, the hot ram will not press upon device 28. Many such devices and particularly the more simple beam lead transistor, have substantial structural strength, and the compliant medium can be caused to deform around the entire device and the leads, thus eliminating the need for a hollow perform 34. This has the further advantage of eliminating any possibility of bending or bugging of the device, although this has not been a problem when bonding with a hollow, compliant preform.

Bonding is illustrated in FIG. 6. A hot ram 36 is pressed down on the assembly, causing deformation of preform 34 and leads 30 in the same manner as described hereinabove in connection with FIGS. 1-3. It will be noted that preform 34 deforms in exact compliance with the leads even when they are very closely spaced. FIG. 7 illustrates the bonded device after removal of the preform.

The extent of deformation of the leads during bonding is apparently a function of the geometry of the compliant medium and the physical properties of the materials, more than anything else. FIGS. l-3 and 4-7 illustrate two shapes of a compliant medium and two somewhat different lead deformations. Where the compliant medium is a sheet which covers essentially the entire lead right up to the device, bonds are made with little or no visible deformation of the lead. The obvious, if not entirely satisfactory, explanation for this is that the energy couple from the source of the interface is, relatively, a broad area one, and a good bond is made with little deformation other than at the interface. In the bonding of beam lead devices, it is preferred to use a solid sheet of the compliant medium which covers the entire device and the leads, when the device is strong enough. Ram pressure is applied overall, the medium deforms around the device and the leads, and makes good bonds. Any tendency toward bugging" is manifestly impossible, since the device and the leads are subjected to the same forces.

The foregoing can be illustrated by a specific example of the bonding of a l6-lead beam leaded device to the Au/T i land areas on a glass substrate. The compliant medium was 2024 aluminum 0.005 in. thick with a square 0.0535 in. hole punched therein. The device was positioned on the substrate and the aluminum was placed thereover, the hole just fitting over the body of the device. The ram was 718 stainless with a flat, lnconel tip heated by a 150 watt cartridge heater. Bonding was carried out for 1.5 seconds with a total ram pressure of about 48 pounds (3 pounds per lead) at a temperature of 400 C. Lateral deformation of the beams due to bonding was less than 10 percent. After bonding, the device could not be blasted loose with 400 psi compressed air. When a sharp probe was used to shear the device from the substrate, all 16 leads broke off and remained bonded to the substrate.

in general, it has been found that successful thermocompression bonds can be made in accordance with the invention at temperatures in the range of 350500 C., bonding cycles of l to even 5 seconds, and ram pressures of 3050 pounds. It will be appreciated, however, that all of these parameters are related. At lower temperatures, for example, longer cycles are in order, and vice versa.

F I68. 8 and 9 illustrate bonding in accordance with a second embodiment of the invention of U.S. Pat. No. 3,533,155. In this embodiment a support or table 38 is provided which is connected to an ultrasonic horn for vibration in a direction parallel to the upper surface. It is convenient to provide a slight depression 40 in the upper surface of support 38 which conforms to the size of the substrate to which leads are to be bonded. A substrate 42 is placed in this depression and, as shown in FIGS. 8 and 9, a beam lead device 44 is positioned thereon. A plunger or clamp 46 has a tip 48 made of an elastically deformable material which is capable of deforming around device and clamping all the leads, regardless of size differences, securely to substrate 42. Plunger 46 can be hydraulic, cam actuated, solenoid actuated, or other suitable means can be employed.

Ultrasonic energy is applied and causes support 38 to vibrate in the direction shown by the arrow in FIG. 9, i.e., parallel to the surface. The bond is made in the conventional ultrasonic manner.

It has been heretofore disclosed that heat can be advantageously applied during ultrasonic bonding with the benefit of preventing work hardening of the leads. The application of heat through a conventional ultrasonic bonding tip creates problems, however, in that the sonic properties of the tip are in part temperature dependent. This problem is eliminated in the present invention because the heat can be applied through plunger 46 and compliant medium 48.

FIG. 10 illustrates the use of a compliant medium, particularly a film-forming metal, as a lead frame for one or more discrete beam lead devices. A rectangular frame 56 having an aperture 58 is provided, into which the device 60 is placed through the bottom, the leads 62 of device 60 being lightly adhered to the underside of frame 56 by use of an adhesive. Alternatively, aperture 58 may be sized so that the body 60 fits snugly therein and is frictionally retained. Indexing marks 64 are provided on the outside of frame 56 and are designed to register with corresponding marks on the substrate to which the device is to be attached. Similar marks (not shown) on the underside of frame 56 will facilitate the accurate placement of the device within the frame. in this manner, proper registration of each lead with its corresponding land area on the substrate is considerably simplified. The dotted lines 65 show how frame 56 may be part of a much larger frame holding a plurality of devices 60. As noted hereinabove, the lead frame may take the form of a long ribbon or tape of the compliant medium. Also, indexing may be accomplished with optical equipment by having small holes in the tape or lead frame.

It will be understood that various changes in the details, steps, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as defined in the appended claims.

What is claimed is:

1. An assembly for retaining at least one device to be bonded, comprising:

a device;

a flat sheet of a material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the thickness of said sheet being substantially greater than the height of said device and said material being a deformable metal or alloy having an adherent oxide film on the surface thereof; and

means securing an upper surface of said device to the under surface of said sheet.

2. The assembly as claimed in claim 1, wherein said sheet is in the form of an elongated tape or ribbon.

3. The assembly as claimed in claim ll, wherein said securing means comprises an adhesive bond.

4. The assembly as claimed in claim 1, and additionally comprising indexing means on said sheet in a predetermined, spaced relation to each device.

5. An assembly for retaining at least one device to be bonded, comprising:

a device;

a flat sheet of a material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the thickness of said sheet being substantially greater than the height of said device; and

means securing an upper surface of said device to the under surface of said sheet, said securing means comprising at least one aperture in said material, each said aperture being adapted to frictionally engage and retain a portion of each device.

6. An assembly for retaining at least one device to be bonded, comprising:

a device;

a flat sheet of a material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the thickness of said sheet being substantially greater than the height of said device; and

means securing an upper surface of said device to the under surface of said sheet, said securing means comprising at least one aperture in said material, each said aperture being slightly larger than a first portion of each device, and an adhesive bond between a second portion of each device and said material around each said aperture.

7. In an assembly for retaining a device to be bonded:

the device; and 1 a flat sheet of a material affixed to the device, the material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the material constituting a deformable metal or alloy having an adherent oxide film on the surface thereof, and the sheet having a thickness substantially greater than the height of the device.

8. In the assembly of claim 7, said sheet taking the form of an elongated tape or ribbon including indexing means in predetermined, spaced relation to the device.

9. A carrier for a device to be bonded, the device having a predetermined height and a predetermined deformability under a given compressive pressure, which carrier comprises:

a flat sheet of material having a substantially greater device to the sheet.

11. A carrier for a device to be bonded, the device having a 10 predetermined height and a predetermined deformability under a given compressive pressure, which carrier comprises:

a flat sheet of material having a substantially greater deformability under said given compressive pressure than said predetermined deformability and having a thickness substantially greater than said predetermined height; and

means for securing the device to the sheet, said securing means comprising an aperture for housing at least a portion of the device. 12. The carrier of claim 11, wherein the sheet takes the form of an elongated tape or ribbon.

PC4050 UNHE STATES PATENT GFFICE QER'HHQAT Qt RECTEN Patent No. 2 ,655 ,177 Dated April 11, 1972 Iiwentofls) Alexander Coucoulas .It is certified that errcr appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the specification, Column 1 (before Objects ofthe Invention" section), the following paragraphshould appear:

-U.S. Patent No. 3,533,155, which issued on October 13, 1970 to A. Coucoulas, concerns a technique bonding workpieces which employs a compliant or deformable medium. The medium acts to hold the workpieces, while transmitting bonding energy to the 1 workpieces and deforming about the workpieces The compliant medium and an assembly, formed by the compliant medium and one or more workpieces carried by the medium, constitute the subject matter-of this invention. A complete background understanding of the use of a compliant medium of this type in bonding workpieces may be had by reference to U. S. Patent No. 3,533,155. Therefore, only a few embodiments of bonding methods, which may employ the medium and the assembly of the subject invention, will be discussed hereinafter.-

Column 2, line 73, "transistor" should read "transistors- Signed and sealed this 8th day of August 1972,

(SEAL) Attest? EDWARD M,FLPTLGHER,J'Ro ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. An assembly for retaining at least one device to be bonded, comprising: a device; a flat sheet of a material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the thickness of said sheet being substantially greater than the height of said device and said material being a deformable metal or alloy having an adherent oxide film on the surface thereof; and means securing an upper surface of said device to the under surface of said sheet.
 2. The assembly as claimed in claim 1, wherein said sheet is in the form of an elongated tape or ribbon.
 3. The assembly as claimed in claim 1, wherein said securing means comprises an adhesive bond.
 4. The assembly as claimed in claim 1, and additionally comprising indexing means on said sheet in a predetermined, spaced relation to each device.
 5. An assembly for retaining at least one device to be bonded, comprising: a device; a flat sheet of a material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the thickness of said sheet being substantially greater than the height of said device; and means securing an upper surface of said device to the under surface of said sheet, said securing means comprising at least one aperture in said material, each said aperture being adapted to frictionally engage and retain a portion of each device.
 6. An assembly for retaining at least one device to be bonded, comprising: a device; a flat sheet of a material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the thickness of said sheet being substantially greater than the height of said device; and means securing an upper surface of said device to the under surface of said sheet, said securing means comprising at least one aperture in said material, each said aperture being slightly larger than a first portion of each device, and an adhesive bond between a second portion of each device and said material around each said aperture.
 7. In an assembly for retaining a device to be bonded: the device; and a flat sheet of a material affixed to the device, the material having a property of deforming to a substantially greater degree than said device when subjected to compressive pressure, the material constituting a deformable metal or alloy having an adherent oxide film on the surface thereof, and the sheet having a thickness substantially greater than the height of the device.
 8. In the assembly of claim 7, said sheet taking the form of an elongated tape or ribbon including indexing means in predetermined, spaced relation to the device.
 9. A carrier for a device to be bonded, the device having a predetermined height and a predetermined deformability under a given compressive pressure, which carrier comprises: a flat sheet of material having a substantially greater deformability under said given compressive pressure than said predetermined deformability and having a thickness substantially greater than said predetermined height, said material being a deformable metal or alloy having an adherent oxide film on the surface thereof.
 10. The carrier of claim 9, including means for securing the device to the sheet.
 11. A carrier for a device to be bonded, the device having a predetermined height and a predetermined deformability under a given compressive pressure, which carrier comprises: a flat sheet of material having a substantially greater deformability under said given compressive pressure than said predetermined deformability and having a thickness substantially greater than said predetermined height; and means for securing the device to the sheet, said securing means comprising an aperture for housing at least a portion of the device.
 12. The carrier of claim 11, wherein the sheet takes the form of an elongated tape or ribbon. 